1. Field of the Invention
The present invention relates to a method and an arrangement for the protection of a transistor, particularly an MOS switching transistor which is located in the lamp circuit of a motor vehicle, by limiting the gate potential and thereby the load current and through monitoring of the source potential whereby, upon deviation from a predetermined value, the load current through the MOS transistor is interrupted, inasmuch as the MOS-transistor is blocked through the intermediary of a switching element having a control input and two load connections, and which is conductively controllable by means of a potential.
Electronic switches for high load currents which, for example, find application in the lamp circuit of motor vehicles, operate with a transistor which is connected in series in the lamp circuit. This transistor must be protected from overload through appropriate measures, when it is desired to avoid the need for oversized transistors. Thus, the current in the lamp circuit should not exceed a maximum value, even in the case when a short circuit is encountered in the lamps.
2. Discussion of the Prior Art
A circuit is presently known which, on the one hand, limits the potential which is present at the base of the transistor through the intermediary of a Zener diode and, consequently, the transistor current between the emitter and the collector, and which, on the one hand, monitors the potential at the collector of the transistor, in order to protect the transistor during the occurrence of a short circuit in the lamp circuit, as is disclosed in Laid-open German Patent Application No. OS 30 15 831. This circuit operates with an ohmic resistance in the lamp circuit, which is sized so that the voltage drop-off thereon, in conjunction with the voltage drop-off at the emitter-base section of the transistor, can exceed the threshold voltage of the Zener diode.
However, the arrangement of an ohmic resistance in the lamp circuit causes an undesireable power loss.